I started this thread on the newbie forum just basically to throw around some ideas. but the more I look into it the more it really gets me confused as to why certain thing wont work. so its time to get technical:

anyways to start why do I want to do this project? well its NOT for pure power or efficiency. So yes i know i can make more power at the same pressure with single turbo vs this complicated set up. BUT what i want is low end trq of a s/c and the high end power of the turbo in a mustang 5.0 302 engine.

that and the fun power all around aswell as the coolness factor if i pull this off lol

anyways so my plan is changing everyday but i want roughly 450whp with this combo. on a stock engine. with maybe a meth kit on a blowthrough 20/80

basically im keeping my 61mm holset h1e and plan to add an older model m90 from a thunderbird.

after researching i scrap my first idea since it would be to complicated and it seems like the only way to pull this off is compound boost or reverse compound boost(i dont know what its called but its s/c first lol)


Lets start with compound boost.

what i was thinking was run a bigger pulley on the m90 and lower the boost to about 4-5. and boost the 61mm to 7psi. now with some weird math it will roughly equal to like i think around 14 or so psi. (im still trying to figure out how to do the equation but its roughly around there.

the first question:
1. Do you think i can run this set up straight without any bypass valve what so ever since the pressure is relatively the same and i think the flow is pretty close.

so basically intake-turbo-s/c-carb. piping will be straight forward.

2. will doing a straight shot for my application work or do i still need to bypass the s/c once turbo kicks in fully?



reverse compound boost. ok so check out the diagram i attached.
basically in front of the turbo theres a Y the bottom of the Y connects to the turbo intake and the top of the Y connects to the s/c and the other connects to a butterfly valve that is boost actuated(like a internal wastegate)

The piping goes as follow.
Intake-s/c-turbo-carb

BUT from the s/c to the turbo there will be another pipe that will open up at like let say 6psi so it basically becomes an open system and the turbo gets its air from the atmosphere and s/c.( so the s/c will loost pressure at this point.) but until that set pressure that link is closed and the s/c feeds the turbo directly.

what do you guys think? will this work?



and Major question. can I use a wastegate as a bypass valve or will it cause to much turbulance since its like an L flow? i cant seems to figure out what to use as a bypass valve.

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Put whatever is biggest (cfm-wise) first in the flow diagram. Also, the 61mm MAY hit 450RWHP, but it will be absolutely maxed out.

You don't have to use the bypass valve. If you do use the bypass valve in the blower, it will be more of a sequential setup than compound boost.

Here is that exact setup:
http://www.performancetrucks.net/forums/forced-induction-159/whine-n-whistle-464822/

 

Im confused if I bypass the s/c when turbo hits full boost its a sequential? but if i keep the system closed and one way run (turbo to s/c to carb) its a compound?

so you think i can just directly run it then and not bother with bypassing the s/c when turbo hits full boost?
I saw the link but i couldnt really see from the pic if he did it this way. looks like he did though.


and yea i figured the 61 is pushing it at that whp but im not set on that number if i can get 400whp with this set up ill be more than happy but its always nice to aim high so the supports parts that i use are up for it. after all this is on an estimated 2700lbs car.

 

Like I said in the other thread, I would do it just like Hellion and feed the supercharger with the turbo. All air goes through both, and the turbo makes the supercharger more efficient by dropping the pressure ratio.

 

They don't bypass the s/c on the hellion right?

 

Nope, right into the supercharger.

 

There is no good way to do compound boost with an M90 and a 61mm turbo. In a compound system the first boost device flows a significantly higher volume of air than the second and must therefore be significantly larger. An M90 cannot feed a 61mm and a 61mm cannot feed an M90.

The mass airflow through the two is the same but the volume airflow is very different.

 

Hmm I thought that the requirement was the 2nd had to flow 2/3 of the first. I haven't seen the flow chart of the m90 but based on acouple 5.0 m90 I saw online it seem to flow around like 80-85% comparing to a 61.

It may not be perfectly 66.66% but its close?

But I could very well be misinterpreting data.

So let's say the air flow is the same: is there no way to make it a compound boost?

So if the flow is the same does that mean if I run it compound style that the total pressure would be the average pressure of the two?
What I mean is if I set booth to 7psi but since they flow the same the total psi can only reach 7? Or will it still be multiplied?


I haven't found an explanation about why the requirement is 2/3. Anyone knows the reason behind it?



Also if the air flow is the same can I then run it parallel? With the turbo being control with a boost valve that would open only when the pressure is even with the s/c?

 

If the second boost device is run around 3.75psi then the first boost device will need to be able to flow 1.25 times more.

If the second boost device is run around 7.5psi then the first boost device will need to be able to flow 1.5 times more.

If the second boost device is run around 15psi then the first boost device will need to be able to flow 2 times more.

It depends on how you do it. Any way you look at it if the second boost device is contributing much at all the first boost device must be significantly larger.

 

Something I will point out is that ultimately the power level of the engine is what determines the behavior of the turbocharger. The more HP an engine produces at N RPM the greater chance that it will spool. There are other factors in play but this is a good "yard stick" to go by. Why I bring this up is that a supercharger artificially increases the power of an engine at a specific RPM. That means in turn you should size the turbo closer to the HP level of the supercharger combo's output not what the engine would make. That means something like a 60-1 or T66 would probably work fine for a stock 302 but if you're making +150hp because you've got a crank driven supercharger (which is RPM dependent, not HP dependent for it's boost curve) then it would require a lot larger turbo to maximize your power. The other thing to keep in mind is that you are "pushing down" the points on your compressor map for the turbo because you are using the supercharger to increase the pressure as well as the supercharger. This is significant because most turbochargers have a "D" shaped island which means they are usually efficient at moderate to higher boost levels for a set compressor size. On the plus side it also tends to push the points over to the right too, so you can use a fairly massive compressor without concern of going into surge.

 

Oh ok, but is a m90 really that big though? Thought it was a relatively small s/c

And do you guys think there is a way to run these two parrallel?

 

That's interesting because I read online somewhere that what the s/c is essentially doing is making the turbo think it's a bigger engine. How accurate is this statement? To me it makes sence.

So sure in regards to efficiency a t66 would work or larger but a 61 would also work wouldn't it? It would just be the restriction b/c it cannot flow?

The reason I ask this is because this build is a street car and fun car but it's also what I call a scrap build and switching to a bigger turbo even to an mp70 would be out of budget. I mean when I buy stuff from friends it's usually me paying them off in labor lol. So I really would like to keep it at a cheap turbo options. Know any? I went holset 61 cuz it's only 200-300 lol

 

I mean lets throw down to the most basic conceptual ideas. These are rough theories but will give the concept well enough.

A)1 atmosphere of boost means that the engine artificially doubles its CFM. That means that you effectively double the CID.
B)lets say you have a basic 302 CID engine.
C)lets run the super at 1.5 atmospheres of pressure absolute (eg about 7.5 PSI) using the crank driven supercharger

What this means is that at 1.5 atms of boost you would be at about 450 CID. Now then, lets think logically here for a moment. If you have a T61 or a T66, would you put a single one on any 450 CID engine? The answer to that is going to be a logical "no."

JMO on this forget the super if you have a 60-1 or T66 with a properly sized turbine. I doubt you will gain much of anything. The spooling of it should be devastatingly effective even with a basic bolt ons engine (cam, intake etc.) and you won't have to worry about parasitic drag of the crank driven supercharger. Not only that but if you have it on hand your additional expenditures are nothing. I'd start out with a turbine in the .68 range and go from there if it's a stock engine. With something like an H/C/I setup the .96 is probably a better bet.

If you had a pair of 60-1s or T66es the combo becomes a hell of a lot more interesting all of a sudden as they would be "large" for a stockish 5.0. You'd have to be running some serious pressure ratios as well as making some nuts power to make it worthwhile though. Levels beyond what you're doing with a stock block by a huge margin.

By the way, an M90 is good for low-mid 300hp if it's the later gen ones used on the 3800s. The rotors are teflon coated which bumps the efficiency up. If they had alky injection it would likely help push the envelope some. I'd rather start with an M112 or a GMC blower though if I was going to the trouble that way I didn't have to spin it nearly as much.

 

Thanks for the info.

But this was what I was talking about. I do understand that turbo will be more efficient. No argument there but if I feel the lag on a 61 there would be more lag if I go bigger. I'm comming from a supra perspective here and quite honestly I have grown to hate lag lol had I known about m90 when I started this project I might have just gone twin m90 since it's would have save me the trouble of making the whole hot side and boost on tap sounds good.

I know lag is minimal compare to my supra but it's there no doubt.

Plus I'm prolly just being a hard head and want a s/c and a turbo lol

In anycase thanks for the drop of knowlege.

You also pointed out the limits of the block. And this is one major concern. 450whp was my original border bc of the block and if I go bigger turbo wouldn't it be a waste really? I mean if a turbo really comes alive at let's say 14 psi running it at 7 to keep the total pressure bellow 20 would make for a "sleeping" turbo. So with the block a major limiting factor wouldnt it best to size up smaller than go bigger and not even touch where the turbo comes alive in?

 

Anyone knows where you put the bov on a compound boost set up?

I figured closest to the carb so after the supercharger, but looking at the stang compound boost they put it between the turbo and s/c I know their s/c is direct to their intake but if it's a separate unit should the bob be placed between turbo and s/c or s/c and carburetor?

 

It will pull out more heat if it is after both.

 

Both

 

Actually if its a PD blower set-up, thats not gonna be feasible, and the blower will have its own built in bypass anyway. So the proper location would be between the turbo and supercharger (if using a PD blower which has been what you are referring to).

Also, you need to figure the pressure ratio for the supercharger at whatever boost level you plan to run and combine it with the pressure ratio of the engine you plan to run (figured at 14.7 atmospheric) and come up with the actual cid consumption the motor thinks it is. A 4.6 liter engine running 8psi of boost from a pd blower is somewhere around the air and fuel consumption rate and there for exhaust gas discharge of a 433 cid engine (give or take). That is how you need to size your turbo as mentioned above.
Find the pressure ratio:
(atmospheric) 14.7 + 8 psi (proposed pd blower boost = 22.7 / 14.7 = 1.544 pressure ratio * engine displacement of 281 cid (4.6 liter for example) = 433 cid consumption rate for 281 cid engine and 8 psi PD blower combined.

 

other than wow factor..
a correctly sized turbo will make engine power to smash the motor to pieces if run at full potentual

is it more of a wow factor build ?

 

is isnt all blower positive displacement? what other type is there?


and Andy was actually nice enough to show me that equation on another post.

basically 4# on an m90 = 384cid

so I was originally going to just run the 60mm but seeing that its spitting more oil than before im planning on running a 76mm.

does an m90 has its own bypass? it would be nice if i can relocate the BOV between the turbo the the blower so i can put the meth kit sooner instead of being right before the cab hat since my bov is only like 12" away from carb hat.



side question my fuel pressure regulator thats boost reference is drawing signal on my carb hat space. between the carb hat and carb will i have problem if i spray before this signal? i mean would methanol enter that hose and cause damage to my fuel regulator?